abse/gameboy-advance

USB_ROUTING_REVIEW.txt

USB DIFFERENTIAL ROUTING REVIEW - v0.0.37

Release v0.0.37 contains the validated USB routing update.
The retained enclosure, component footprints, power-switch location, display
connector, real supplier models, and buttons are unchanged.

Long connector-to-27-ohm-resistor paths are paired on L1 with no signal vias.
The primary D- contact is B7 and D+ is A6; the other USB-C duplicate contacts
remain tied correctly through their short breakout branches. Both termination
resistors remain in their original positions near RP2350.

Nominal geometry: JLC04161H-3313, 90 ohm coplanar differential, L1 over L2;
0.131318 mm width, 0.15 mm pair gap, 0.18 mm gap to coplanar ground.
Supplier calculator: https://jlcpcb.com/pcb-impedance-calculator
Stackup: https://jlcpcb.com/impedance
RP2350 guide, section 5.1:
https://datasheets.raspberrypi.com/rp2350/hardware-design-with-rp2350.pdf

Short resistor-to-MCU escapes remain the original routes: D- approx. 2.03 mm,
no vias; D+ approx. 4.27 mm, two vias. These breakouts do not have a controlled
90-ohm differential geometry. At 12 Mbps, the approx. 1.60 mm mismatch between the primary B7/A6 paths is small; actual USB compliance/eye testing has not been performed.
The paired trunks measure D- 47.38 mm and D+ 46.73 mm (0.65 mm skew).
Including the duplicate-contact stubs and chip escapes, the A6/A7 plug path
has 3.66 mm skew and the B6/B7 path has 3.95 mm skew. These are PCB path
estimates, not measured USB timing. Do not describe the entire USB path as
via-free or USB-certified.

Neighboring trace branches were adjusted to preserve clearances and ground
reference under the long USB pair. Power-path widths were preserved. Generated
via endpoint port IDs were removed from authored routes because deleting or
adding vias changes those virtual IDs; actual component endpoints remain.
No DRC, spacing, via-size, or maximum-length limits were relaxed.

The full local build and independent all-layer Gerber short check pass.
Exact polygon subtraction finds zero missing L2 ground under both paired
trunks. All component PCB positions, rotations, layers and footprint
dimensions match published v0.0.36.

Validation evidence is under dist/index: validation.json, physical-checks.json,
physical-connectivity.json, usb-differential-routing.json, and schematic reports.
The retained 23 requested-width warnings are separate from errors.